The invention relates to the transmission of data via radio signals. More specifically, it relates to the provision of an in band radio control channel.
In a network of information systems, such as computer systems and telephony devices, any communication between two nodes of the network generally contains two distinct types of data: 1) user data that is intended to go from one node to another, and 2) communications overhead data that is used to facilitate movement of the user data between nodes. Since the communications overhead data is only needed for communication, it is generally created by a sending communication interface device, such as the sender""s network interface card (NIC), modem, and/or other device, before transmission and deletion by a receiving communication interface device, such as the receiver""s NIC modem and/or other device after reception. Therefore the user computer or other termination device never sees the communications overhead data and may be unaware of its existence. (Note: In the context of this document, the terms xe2x80x98user computerxe2x80x99 and xe2x80x98user dataxe2x80x99 do not necessarily imply a human user. They refer to the devices, such as computers at the node which perform the various functions that the node exists to handle, and the data that those devices transfer to each other. The terms are defined in this manner to distinguish between the data transferred between network nodes and the data used only to facilitate the communications process.)
There is another type or layer of data, however, that does not fall within either category, and which can be generically called network overhead data. This can include network management information, which is data that can be used to improve the overall operation of the communications network as provided through the various links comprising the network. Since this data is not native to the individual point-to-point communication, the communication interface devices, such as the aforementioned links and modems, do not comprehend it. But since the data is related to the communications function, it is not user data and typical user software does not comprehend it either. Even if the user computer can be programmed to identify this network information and insert it into or remove it from the user data, the use of very high speed communication links would put a burden on the user computer that most are unable to handle. The use of radio links, with typical speeds of hundreds of megabits per second, renders the user computer completely inadequate for this task. Moreover, in addition to the user typically not wanting to share bandwidth available to the user with communication network data, the communication network provider, or other system administration, does not want the user (or user equipment) to have access to this overhead data.
With conventional systems this additional layer of information, if implemented at all, is typically transmitted separately. This might take the form of a separate network, such as through separate links to link apparatus, through a separate network, such as a public switched telephone network (PSTN) and/or a discrete link, such as in the case of radio where a discrete link frequency channel provides a second link. Either option requires the expense of secondary equipment just to monitor or operate the primary equipment. This additional equipment will also have its own operational and reliability problems, further adding to the cost of maintaining the overall system. It would be preferable to transmit this information over the same link that is used for communicating user data. However, standard communication interface devices do not include this type of information and do not provide a way to incorporate it into the communication overhead data.
Much of the difficulty is caused by the predetermined operation of the communication interface devices, such as a modem. Communications overhead data typically is often used to enable link reliability functions such as error detection and/or correction. These functions are used to detect errors in the bit stream that may have occurred during transmission, and to correct those errors in the received data. Error detection/correction may take various forms, but in general is implemented by using an algorithm to derive additional data from the user data before transmission, transmitting this additional data with the user data, and then repeating the algorithm on the received user data to see if it produces the same result as the received additional data. If the results match, the received user data is assumed to be error-free. If the results do not match, the format of the additional data permits limited correction of user data through reconstruction algorithms.
This error detection/correction function is typically implemented by the communication interface devices such as the above mentioned modems. Accordingly, the additional data is referred to herein as xe2x80x9cmodem overhead dataxe2x80x9d as well as communication overhead data. Although it shall be appreciated that similar data or other data useful in providing desired communication, such a routing information, etc., may be provided by other forms of communication interface devices, such as the aforementioned NICs.
Communication interface devices, such as modems, also typically implement xe2x80x9cframexe2x80x9d transmission, which may be utilized to facilitate the above mentioned error detection/correction, dividing the data into continuously transmitted discrete frames of a predetermined size and format. The predetermined frame format allows the receiving communication interface device to know where to look within each frame for modem overhead data and user data. Unfortunately, each type of communications standard (Ethernet, Fast Ethernet, SONET, radio, etc.) has developed different format/ framing standards, and extensive conversion may be needed when data is successively transmitted through different types of communications links if this communication overhead data is to be shared among the successive devices.
Regardless of the communications standard used, each transmission which utilizes the above described overhead data frame can be considered to have two distinct data parts: payload data and modem overhead data. The payload data is the data presented to the communication interface device for transmission. The communication overhead data is the additional data added by the transmitting communication interface device and removed by a receiving communication interface device. User computers typically do not see any communication overhead data and are functionally unaware of its existence. Therefore, the communication of user data through a pair of such communication interface devices appears to the user as a stream of user data, although it may actually be broken up to fit particular framing standards and have communication overhead data appended thereto.
Communication interface devices, such as modems, can also make use of additional techniques to ensure that the frame occurs in a periodic manner such that two communicating devices are always in synchronism with respect to the beginning and end of a modem frame. Because the frame format is known, the devices always know where the location of payload data and communication overhead data, such as error correction data is located relative to the beginning and end of each frame. Some communications standards require that frames be transmitted synchronously and continuously, even if there is no user data to transmit. In those cases, xe2x80x98emptyxe2x80x99 or xe2x80x98nullxe2x80x99 user data must be substituted during those periods of idleness. Since user data may be presented for transmission at any time, and may be framed differently than the modem requires, techniques are required that both synchronize and reframe the data.
In addition to the above mentioned communication overhead data, information useful in controlling aspects of the network and/or its various links may be desired. For example, where a link is provided through wireless means, the above mentioned communication overhead information may be insufficient to provide desired communication characteristics. Specifically, as radio frequency communications are attenuated due to atmosphere conditions, signal fades and in extreme conditions signal loss may result which simply is not addressable by the communication overhead information such as error correction techniques. Accordingly, a communication system overhead channel, such as a radio overhead channel may be desired which places the radios of a wireless link in communication with one another in order to allow information regarding the need to increase a transmission power level to compensate for a change in received signal characteristics, such as due to a change in atmosphere conditions. As there must exist a link to provide the user data link, it would be preferable that the radio overhead channel or other network link overhead channel be provided through this user data link. However, due to the above mentioned link data structure requirements, such as framing, it is difficult to transport additional overhead data in band without consuming user payload bandwidth.
Additionally, in order for the transmission of the communication interface device to appear transparent to the user, it is desired that its throughput of user data match that of the termination device, irrespective of the addition of overhead data, in order to avoid delays and accumulation of user data at the transmission point. Accordingly, the addition of in band network overhead data becomes further complicated.
Considering the aforementioned problems with conventional systems, it is desirable to provide an economical interface that can transmit and receive network overhead data over the same channel used to communicate payload and communication overhead data, while providing all the necessary synchronization and framing conversions. It is particularly desirable to provide this interface for radio link communications, where such network technology is relatively undeveloped.
A solution to the aforementioned problems in the prior art is achieved by a system and method which places specialized overhead data into the payload data before presentation of the payload data to a communication interface device, such as a modem. The data is placed in such a manner as to cause each frame to contain the overhead data in the same location and format, i.e., providing a network overhead data frame within a communication interface device frame to enable predictable in band transmission of network overhead data which may be easily multiplexed and demultiplexed from other transmitted data. A multiplexing/demultiplexing device providing a user data interface, a link overhead data interface, and a communication interface device interface, such as a specially adapted network interface card (NIC) can be used to insert/extract this overhead data into/from the payload so that the communication interface devices see it as payload data, while the associated user computers do not. This overhead data might be generated by a network controller such as a centralized network operations center and/or a distributed network controller associated with a particular link or subset of links of a network. Additionally, or alternatively, this overhead data may be generated by the multiplexer/developer device, or control logic operable therewith, or the user computer possibly in response to a monitored attribute such as a measured bit error rate in the received user data or a triggering event such as a particular number of requests to resend a particular data packet. In a preferred embodiment, the network uses radio links for communication and this overhead information is referred to as radio overhead data.
It is an object of the invention to provide an interface that will embed or multiplex special overhead data into the payload data of a communication interface device transmission stream, such as a modem frame. Accordingly, it is an object of a preferred embodiment of the invention to provide an interface that will embed radio overhead data into the payload data of a radio modem frame.
It is a further object of the invention to provide an interface that will extract the special overhead data from the payload data of a communication interface device received data stream, such as a modem frame. Accordingly, it is an object of a preferred embodiment of the invention to provide an interface that will extract radio overhead data from the payload data of a radio modem frame.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.